Glenn I found the following on SH.
not sure if this has been posted already. very basic (and in some cases out of date) explanation of
fuel cell basics and also the problems facing car companies in trying to replace ic engine with
hydrogen based pem fc's for propulsion.
cnet.com
By Stephen Jacobs
(11/22/00)
November 1 marked the opening of the headquarters of the California Fuel Cell Partnership. To
mark the occasion, representatives of DaimlerChrysler, Ford, General Motors, Honda, Hyundai,
Nissan, Toyota, and Volkswagen brought their exotic, prototype fuel-cell-powered cars and buses
to show off. These manufacturers are banking on the hope that the real car of the future won't be
the battery-operated and hybrid gas/electric cars, which are offered now as low-polluting vehicles,
but rather, cars running on a technology with its roots in an idea that's more than 150 years old.
Getting a Charge Out of Classical Gas
In high school science, you probably performed electrolysis on water, where you ran electricity
through water to separate the hydrogen from the oxygen. In 1800, William Nicholson and Anthony
Carlisle were the first to do this. Thirty-nine years later, Sir William Grove suggested that there
might be a way to turn this process upside down and create electricity by bringing hydrogen and
oxygen together. More than one hundred years later, NASA began pursuing an electrical power
plant in an effort to provide the energy for its rockets to ultimately take man into outer space. The
organization began funding research into fuel cells (systems that would successfully and reliably
do what Grove had envisioned) as a power source. And in the early 1960s, functional fuel cells
were heading into space.
The fuel cells used by automobiles work by grabbing oxygen from the air and combining it with
hydrogen, which is either stored onboard or extracted as needed from hydrogen-rich fuels, such as
gasoline. Here's how these cells function: Hydrogen and oxygen are introduced on opposite sides
of a membrane. The two elements are attracted to one another, and the hydrogen molecules try to
pass through the membrane to get to the oxygen. As they pass through the membrane, their
electrons are stripped off and pass around the membrane, creating an electrical current. On the
other side, the hydrogen combines with the oxygen to create water and heat. One fuel cell
produces one volt (give or take .3 volts, depending on the electrolytes and catalysts used). By
stacking a lot of cells together, you produce a lot of volts. Pile enough of them together and you
can power a car or something even bigger.
All the World Loves a Fuel Cell
Despite all the hoopla that automobile companies have generated over fuel-cell cars, public
transportation and industry aren't lagging, either. In the past year, Canada and Chicago have both
conducted mass-transit bus trials. Plans have also been announced to produce power plants,
mining locomotives, and oceangoing vessels all using this energy source.
And with a fuel cell, there's no reason why a power plant couldn't be right beside your home. Two
years ago, Plug Power stuck a refrigerator-sized fuel cell, which was able to supply a residence
with all of its power needs, outside an Albany, New York, home. The demo home originally
extracted the necessary hydrogen from gasoline through a process called reforming. In 1999, this
system was successfully converted over to natural gas, meaning the technology could easily be
adapted to many homes currently supplied with natural gas. General Electric MicroGen inked an
agreement with Plug Power to distribute its home units and expects to start distributing the
HomeGen 7000, a 7-kilowatt unit, in 2001. The company also plans to offer an expanded line of
units for the home in the following year.
Tiny fuel cells are also in the works. Manhattan Scientifics in Los Alamos, New Mexico, is
developing a product dubbed the MicroFuel Cell, which it hopes to sell as a power source for cell
phones. It showed off its first methanol-powered prototype about a year ago, and it displayed a
holster for recharging a cell-phone battery at the 2000 Fuel Cell Seminar in Oregon.
Imagine "recharging" your cell phone, PDA, or MP3 player with a syringe full of windshield-wiper
fluid (windshield-wiper fluid is methanol and water). Too cool. The company is also working on a
fuel-cell-powered bicycle.
Sounds too good to be true, So What's the Catch?
Unfortunately, there are several snags in this grand-sounding plan. Up until now, the biggest
hurdles were the size of the fuel cells, the cost of manufacturing them, and the efficiency of these
systems. However, as more research is done, the fuel cells themselves are getting smaller,
cheaper, and easier to manufacturer.
Although there are several different types of fuel cells, the Proton Exchange Membrane (PEM) is
the most popular type with automobile manufacturers for practical reasons. Even though it is
actually less efficient than fuel cells using other electrolytes, such as phosphoric acid, carbonate,
and solid oxide, its cooler operating temperature is better suited to powering a vehicle. PEM fuel
cells run at 80 degrees centigrade, while the other fuel cells run at temperatures of 200, 650, and
1,000 degrees centigrade, making them impractical or impossible to use in cars, despite the fact
that cells are more efficient the hotter they get.
editorial comment:
(obviously these guys haven't heard what bmw/delphi/gle are doing with sofc's)
The biggest problem now is where to get the hydrogen required by the fuel cell. There are two
main schools of thought here. The first is to provide the cell with a hydrogen-carrying fuel and
have it convert (in the process called reforming) the hydrogen as it runs. The three fuels being
looked at most closely are gasoline, natural gas, and methanol. Each has its drawbacks,
though--especially methanol, which in its pure form is wildly toxic and can insinuate itself in a local
water table with ease. Gasoline and natural gas are good choices because we already have the
infrastructure to supply these fuels to cars and homes. However, they're fossil fuels. There's some
discussion of hydrogen peroxide, landfill gases, and biomass as alternative sources.
The other option is to start with hydrogen. Unfortunately, putting this particular tiger in your tank
also has its problems. Hydrogen doesn't squeeze into a gas tank easily and has a tendency to
leak out of most containers due to the small size of the molecule.
Still, the hydrogen storage issue is a problem that engineers and chemists will likely be able to
work out over time. As far as supply goes, perhaps we'll play it smart and take a low-impact
approach for once. Maybe we can avoid massive chemical reforming of other fuels for their
hydrogen and develop more planet-friendly approaches to hydrogen generation instead. University
of California, Berkeley scientists have coerced algae into producing hydrogen during
photosynthesis instead of oxygen. Their press release from this past February suggested that "A
single, small commercial pond could produce enough hydrogen gas to meet the weekly fuel needs
of a dozen or so automobiles."
Imagine fleeing the city years from now to retire and start a hydrogen farm. You'll fill a barn with
rows and rows of well-sealed hydroponics trays and grow lights and will bleed off the trays once a
day to a storage tank. Once a week the fuel company truck pulls up, empties your tank, and
leaves a check. Or perhaps you could put that high school experiment to the test: Put a mess of
solar panels on the roof of the barn, install a well-sealed swimming pool into the barn floor, and
run wires from the roof to the pool. As in the old experiment, applying an electric current to water
generates hydrogen and oxygen. Filter out the hydrogen into a tank, and you might be able to
receive a check from the same guy who visits the algae farms.
Ten years or so and who knows? Perhaps fossil-fuel technology will join the fossils. If it does, we'll
all breathe easier.
overall, they at least point out the problems with pem and the time frame before they might be
commerically viable. when the near term advantages of sofc vs pem (and gle's sofc in particular),
become more widely known, we should hopefully see more comparable valuations. |
